The goal of this research is to elucidate the regulatory mechanisms involved in allosteric control of enzyme activity. Using biochemical and genetic techniques we are examining the structural organization and catalytic efficiencies of enzymes when they interact with cellular metabolites. Specifically, we are investigating the catabolite inactivation of biodegradative threonine dehydratases from Escherichia coli and Salmonella typhimurium by pyruvate and glyoxylate. A separate aspect of our study includes the role of mercaptide bonds as they influence the conformational change and catalytic potential of homoserine dehydrogenase of Rhodospirillum rubrum.